Now, when I do an ldapsearch for the uid=dusty, with -a always, I get no
results.

That's correct, because the entry being referred to doesn't match your
search filter. I.e., you're searching for entries with a filter
(uid=dusty) and the accountNumber=1 entry doesn't satisfy this filter.

There's no evidence that aliases are misbehaving here, you just need to
think more clearly about the requests you're issuing and what you want
to accomplish.